Adsorption kinetics in micellar solutions of nonionic surfactants

Standard models of the adsorption kinetics of surfactants at the air-water surface assume that micelles break down into monomers in the bulk solution and that only monomers adsorb. We show here that micelles of the nonionic surfactant C14E8 adsorb to the surface of a liquid jet at a diffusion-controlled rate. Micellar adsorption can be switched off by incorporation of a small amount of ionic surfactant into the micelle and switched on again by addition of salt. More sophisticated models of adsorption processes in micellar solutions are required that permit a kinetic flux of micelles to the air-water interface.     

Small angle neutron scattering study of two nonionic surfactants in water micellar solutions

Two classic nonionic surfactants — C₁₄E₇ (heptaethylene glycol monotetradecyl ether) and C₁₀E₇ (heptaethylene glycol monodecyl ether) were investigated in heavy water solution for concentration c = 0.17% (dilute regime) at different temperatures in the range t = 10–35°C by small angle neutron scattering (SANS) method. In the case of C₁₄E₇ surfactant — for all temperatures at c = 0.17% there are two axial ellipsoidal micelles with longer axis 15 nm at 10°C and 49.5 nm at 35°C in investigated solutions. For C₁₀E₇ surfactant at the same concentration of solution and temperature — two axial ellipsoidal micelles were observed, too. The longer axis is equal to 7.5 nm at 10°C, 9 nm at 20°C and at 35°C this axis is equal to 12 nm. Micelles of C₁₀E₇ nonionic surfactant are smaller than those of C₁₄E₇ surfactant in the same experimental conditions.      

Mixed micellar aggregates of nonionic surfactants with short hydrophobic tails

Mixed micelle formation by aqueous mixtures of pentaethylene glycol monohexyl ether (C₆E₅) and diethylene glycol monohexyl ether (C₆E₂) has been investigated by determining the temperature-composition phase diagrams and measuring the intradiffusion coefficients. In binary aqueous solutions, C₆E₅ shows a high tendency to micellize, while C₆E₂, because of its too short hydrophilic head, presents a macroscopic phase separation in a water-rich and a surfactant-rich phases. The temperature-composition phase diagrams obtained for the ternary water-C₆E₅---C₆E₂ mixtures present a micellar region in which both surfactants co-aggregate. The dimensions of this micellar region depend on the relative ratio between the two surfactants molalities. By analysing the micelle intradiffusion coefficient, measured through the PGSE-NMR technique, the hydrodynamic radius of the aggregates has been estimated at 25 °C. It is similar to that of triethylene glycol monohexyl ether (C₆E₃) in binary aqueous solution. The experimental evidences suggest that in mixed ethoxylated surfactants the micellar behaviour is mainly determined by the mean number of ethoxylic units per surfactant molecule, independently of their distribution.     

Small-angle neutron scattering study of the structure of mixed micellar solutions based on nonionic and two cationic surfactants

The aggregation in mixed water systems based on nonionic surfactant, i.e., heptaethylene glycol monotetradecyl ether (C14E7), and cationic surfactants, i.e., cetyltrimethylammonium bromide (CTAB) and cetyltrimethylammonium chloride (CTAC), has been investigated using the small-angle neutron scattering method. The preliminary results of the study of the behavior of C14E7 aqueous solutions (for a concentration of 0.17%) when adding various small amounts of classical cationic surfactants (CTAB and CTAC) have been presented.     

Critical anomaly in the viscosity of a nonionic micellar solution

The critical enhancement in the viscosity has been examined using a low-shear rotational viscometer for a nonionic micellar solution of tetraethylene glycol n-decylether (C₁₀E₄) in water. The estimated value ø=0.041±0.005, which characterizes the temperature dependence of the viscosity very close to its critical point of mixing, is in excellent agreement with that predicted by the dynamical universality for a fluid.     

Excitation energy transfer in chromophore aggregates within a dissipative medium

The Redfield theory-based model of excitation energy transfer in chromophore ensembles within dissipative environment is proposed. Application of the multipole expansion to an operator of interaction between the chromophore molecules and the environment together with some assumptions about the latter led to the closed-form expressions for the elements of the dissipation tensor. These expressions relate the rates of transition between eigenstates of a chromophore ensemble with the spectral and electronic properties of an environment and the chromophore molecules. For several model cases the exact solution of the Redfield equations was obtained.     

Processes of electronic excitation energy transfer between luminescent dye molecules in microheterogeneous systems based on polymer micellar solutions

The processes of electronic excitation energy transfer (EEET) between different-type dye molecules in polymer micellar solutions with different polyelectrolyte concentration have been analyzed. The possibility of regulating the EEET efficiency between dye molecules due to change of the structure of polymer micellar complexes has been established. The results presented are explained from the viewpoint of the fractal character of distribution of interacting particles. The experimental dependence of the fractal dimension of the distribution of dye molecules in polymer micellar solutions on the polyelectrolyte concentration has been obtained.     

Viscous mhd solutions with no transfer of energy through the spectrum

Exact space periodic solutions to the viscous magnetohydrodynamics equations with arbitrary vector periods p₁, p₂, p₃ are derived. A complete classification of the p_j-periodic MHD solutions with pairwise noninteracting Fourier modes is obtained. The solutions have no transfer of energy through the spectrum and are smooth for all values of the time variable t ≥ 0.     

Excitation energy transfer between photosystems in the cyanobacterium Synechocystis 6803

In cyanobacteria, the light-harvesting complex phycobilisomes (PBS) can transfer the harvested energy to photosystem II (PSII) and photosystem I (PSI) and from PSII to PSI. The efficiency of energy transfer from PBS to PSII or PSI, as probed by the ratio of the fluorescence yield of PBS to that of PSII or PSI, was similar in static and aerated cultures of a cyanobacterium Synechocystis sp. strain PCC 6803. In contrast, the fluorescence yield for PSII was notably high while that for PSI was remarkably low in static cultures when compared to that in aerated cultures. Additionally, the level of the efficiency of excitation energy capture by open PSII reaction center was markedly decreased in static cultures in comparison to that in aerated cultures. Thus, the energy transfer from PSII to PSI, but not from PBS to PSII and PSI, was inhibited in static cultures and was most likely caused by the reduction of PSII activity.     

Tip streaming from a drop in the presence of surfactants

Drop breakup in a linear extensional flow is simulated numerically using a nonlinear model for the surface tension that accounts for maximum packing at the interface. Surface convection sweeps surfactant to the drop poles, where it accumulates and drives the surface tension to near zero. The drop assumes a transient shape with highly pointed tips. From these tips, thin liquid threads are pulled. Subsequently, small, surfactant-rich droplets are emitted from the termini of these threads. The scale of the shed drops depends on the initial surfactant coverage. Dilute initial coverage leads to tip streaming, while high initial coverage leads to the tip dropping breakup mode.     

Characteristics of second harmonic generation in sequentially positioned crystals with strong energy transfer

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 53, No. 3, pp. 364–370, September, 1990.